Description.
Here is the circuit diagram of a simple subwoofer filter that can be operated from a 12V DC supply. Such a circuit is very useful in automobile subwoofer applications. The circuit is nothing but a low pass filter whose pass frequency can be adjusted between 60 to 160 Hz.
The circuit is designed around the TL072 dual BIFET opamp IC. Out of the two opamps inside the chip, IC1A is wired as a buffer. The left and right audio inputs after mixing is fed to the input of the IC1A using the DPDT switch S1. Switch S1 is the phase control switch which can be used to make the subwoofer in phase with other speakers. When S1 is in position 2, 180 degree phase shift will be induced.POT R7 can be used for controlling the level. IC1B forms the low pass filter whose pass frequency can be controlled by adjusting the dual gang POT R13.

If you want powerful sub-sub sound, put a linkwitz filter on the front end. This will overcome a poor performing speaker by putting a gain boost on the lower frequencies. If your speaker rolls off (for example) below 40Hz, you can make it perform down to 20 HZ if you want using the linkwitz filter.

can the inout be from any weak audio source or does it need to be pre-amplified? because it provides weak bass as compared to the other two channels. I made a 3 channel amplifier and fed output of this circuit to 3rd amp.
I used this amp circuithttp://www.circuitstoday.com/car-stereo-circuit-using-tda2040

hi, im ashok
1,do we need to amplify the subwoofer output or we can feed it directly to it?
2,if we have to amplify it ,then wats the amplifier circuit?
3,moreover the pin 8 is supply but it is connected to 3rd pin via 100k, is that rite?
4,is the input is preamp input or amplified input?

yes you need to amplify its out because this circuit is only a filter and has very few mili volts output… so it must be definitely amplified.
There is no specific circuit for this amplifier you can use it at the input of any amplifier